(Health.com) -- Roughly two-thirds of adults and one-third of children in the U.S. are now overweight or obese. Aside from contributing to rising rates of diabetes and other chronic illnesses, this widespread weight problem also appears to be changing our perception of what's considered heavy.

As overweight and obesity have become more common, those who are carrying unhealthy extra pounds are increasingly likely to see their weight as normal, and are therefore unlikely to feel the need to shed some of those pounds.

The latest evidence for this trend was presented Wednesday at an American Heart Association conference in Atlanta, where Columbia University researchers reported the preliminary results of a study that found that overweight mothers and children tend to underestimate their own -- and each other's -- weight.

"A lot of their misperception has to do with the fact that overweight and obesity is becoming the norm," says the lead author of the study, Nicole E. Dumas, M.D., an internal medicine resident at Columbia University Medical Center, in New York.

The study included 222 mostly Latino mothers and children who were recruited at a children's health clinic in an urban setting. The research team interviewed the participants about their medical history and social background, and also measured their height, weight, and body mass index.

Just under two-thirds of the mothers were overweight or obese, as were nearly 40% of the children, who ranged in age from 7 to 13. The vast majority of the overweight people weighed more than they thought they did -- and the heavier they were, the more likely they were to underestimate their weight.

Eighty-two percent of the obese women underestimated their weight, compared with 43% of overweight and 13% of normal-weight women. Likewise, 86% of overweight or obese children failed to correctly estimate their weight, compared with just 15% of normal-weight children.

"There was a trend that showed that as women became more and more overweight, and then obese, the larger the misperception of true body weight was," says Dumas. "Unfortunately, we found this was the case with the children as well."

The participants' misperceptions were not limited to how they viewed themselves: Nearly half of the mothers who had an overweight child believed their child's weight to be normal. And even though more than 80% of the women were overweight, only 41% of the children thought their moms needed to lose weight.

Moreover, when the children were presented with a series of cards bearing silhouette images of body types and were asked to select the "ideal" or "healthy" size for their mother, they tended to pick body types that were, in fact, unhealthily large.

Robert Eckel, M.D., a cardiologist and professor of medicine at the University of Colorado Denver, says the study was too small and too ethnically homogenous to support any firm conclusions. "With this fairly small sample, it's hard to weed out any information that is generalizable," says Eckel, who was not involved in the research. "However, it's clear that perception was skewed."

Dumas acknowledges that her findings may not apply to the U.S. population as a whole, although she points out that other studies have found similar trends among African Americans and Caucasians. The study does, however, shed much-needed light on how weight perception functions across generations, she says.

"In order to target the obesity epidemic, we need to improve perceptions of body weight and create healthy image goals," Dumas says. "But how do we change perceptions? That's the big question."

Dumas presented her findings at the American Heart Association's annual conference on nutrition, physical activity, and metabolism. Unlike the studies published in medical journals, the research presented at the meeting has not been thoroughly vetted by other experts.